1. Field of the Invention
The present invention relates to a system that controls the driving force imparted from an actuator to an element to be driven, such as a link connected to a joint of a robot.
2. Description of the Related Art
As a power unit that drives a joint mechanism of a robot or the like, there has conventionally been known a power unit in which a spring member is interposed between an output section of an actuator and an element to be driven, such as a joint mechanism, and which is adapted to control the actuator such that the driving force (a translational force or a moment) applied to the element to be driven follows a desired value.
This type of unit is described in, for example, Japanese Patent Application Laid-open No. 2001-195133 (hereinafter referred to as Patent Document 1) or “High-Fidelity Joint Drive System by Torque Feedback Control Using High Precision Linear Encoder/Tomohiro Kawakami, Ko Ayusawa, Hiroshi Kaminaga, Yoshihiko Nakamura/2010 IEEE International Conference on Robotics and Automation Anchorage Convention District/May 3-8, 2010, Anchorage, Ak., USA” (hereinafter referred to as Non-Patent Document 1).
In the foregoing power unit, the driving force is usually transmitted from the actuator to the spring member through the intermediary of a power transmission element, such as a reduction gear.
In this case, the power transmission element, such as a speed reducer, is more rigid than the spring member. However, the power transmission element, including the reduction gear, generally has a certain level of springiness, and the springiness of the power transmission element may give rise to the oscillation phenomenon of the driving force applied to the element to be driven.
Further, Patent Document 1 mentioned above, for example, proposes a technique for suppressing the backlash oscillation of a gear, which serves as the power transmission element, by using an observer.
However, the technique described in Patent Document 1 does not take into account the influences of the rotational friction or the viscosity or the like of the output shaft of the actuator. Hence, the influences may prevent the driving force, which is actually applied to the element to be driven, from following a desired value.
Meanwhile, a technique for compensating for the influence of the friction by using the observer has been proposed in Non-Patent Document 1.
The technique, however, does not take into account the springiness of the power transmission element, such as a reduction gear, interposed between the actuator and the spring member. Therefore, the driving force actually applied to the element to be driven may develop the oscillation phenomenon or the like due to the influence of the springiness.